This invention relates to a dimming device and a searchlight with a dimming device.
Such dimming device serves to mechanically dim the brightness of a light field generated by a searchlight, in order to adjust and possibly reduce the brightness of the light field, and for this purpose includes one or more screening elements adapted to at least partly screen the light emitted by the searchlight. Such dimming devices are used in particular in high-performance searchlights, which can for instance constitute daylight searchlights or ceramic searchlights, in order to adjust the brightness of the light field generated, and are advantageous for instance as compared to presently known electronic ballasts, which only to a restricted extent can be used for dimming high-performance searchlights, since they influence the operating behavior of such searchlights and change the color temperature of a searchlight when dimming the same. Therefore, known electronic ballasts only provide for dimming in a very limited dimming range or do not provide for dimming at all.
In particular in television studios, however, it is absolutely necessary to provide for dimming in a dimming range between 0% (no dimming) and 100% (complete darkening) with a homogeneous distribution of light, so as to be able to reproducibly adjust a certain light field.
From DE 299 16 992 U1, a mechanical dimming device in the form of an adjustable multiflap shutter for lighting equipment, in particular for studio searchlights, is known, in which a number of lamellae are rotatably mounted in a frame. By means of a manually or power-operable adjusting mechanism, the lamellae can be moved here between a completely closed position of the multiflap shutter, in which the edge portions of the lamellae overlappingly lie one above the other, up to a completely open position, in which the lamellae are aligned vertical to the front disk of the searchlight. With a constant luminous intensity of the searchlight, the brightness of the light field generated hence can be adjusted from zero with completely closed lamellae to almost the full luminous intensity emitted by the lamp with open lamellae, due to the angular adjustment of the lamellae. The lamella system can be formed either with parallel lamellae or with lamellae arranged radially with respect to each other, which lamellae can be provided with a ceramic coating, in order to prevent a deformation of the lamellae due to the heat produced also in the case of high-performance searchlights.
Such dimming devices constituting multiflap shutters can lead to an undesirable influence on the light field generated by the searchlight. In particular, such multiflap shutters allow a stepless dimming of the brightness of the light field generated, but they cause irregularities, for instance in the form of strip patterns, in the light field generated, which also are dependent on the focus adjustment of the searchlight. Since the multiflap shutters in addition include supporting structures in the form of webs or axles for holding the lamellae and the lamellae are changed in terms of their alignment, but are not removed from the region of the light emitted by the searchlight, a complete brightening, i.e. a light field with the maximum luminous intensity produced by the searchlight, is not possible. If finer lamellae are used, the strip patterns in the light field can be reduced, but due to the required greater number of lamellae, the maximum adjustable brightness is further reduced.
Other dimming devices, also referred to as “stepped density filter” and “variable density filter”, employ screening elements for instance in the form of optical wedges arranged on a glass disk, which are tapered in one direction and for dimming a searchlight are shifted into the region of the emitted light such that for adjusting a great brightness, the narrow portions of the optical wedges are positioned in the region of the light, and for adjusting a small brightness, the wide portions of the optical wedges are shifted into the emitted light, so as to achieve on the one hand a weak screening and on the other hand a strong screening of the light. Such screening elements can constitute, for instance, rectangular plates movable relative to a searchlight or circular elements rotatable relative to the searchlight, with the brightness being adjusted by a change in position of the screening element relative to the searchlight. Furthermore, instead of the optical wedges, a continuously changing grey distribution can also be provided on such screening elements. In such dimming devices, it is disadvantageous that the screening element used must be formed at least twice as wide and high as the light outlet opening of the searchlight—preferably even greater by a multiple—for adjusting a neat light distribution in the light field.
From DE 199 46 015 A1, a dimming device is known, in which for adjusting the brightness of a light field generated by a searchlight two perforated grids are used, which are shifted relative to each other for regulating the brightness of the light field. In this way, a stepless adjustment of the brightness of the light field is possible, wherein the brightness can, however, only be regulated within a very small range and cannot be darkened completely.
U.S. Pat. No. 4,037,097 relates to a slide changer for a lighting system for replacing filters or also mechanical dimmers, which includes a housing enclosing a plurality of disks and a mechanical swinging means. By the swinging means, the slides are moved before the lightfield of a spotlight or removed from the light field as desired.
EP 0 017 210 A discloses a searchlight, which in a searchlight housing includes an arrangement for holding a lens and a shutter holding device. The shutters can be moved from outside by means of handles and be adjusted in their position.
From U.S. Pat. No. 6,076,942 an arrangement for generating a homogeneous light field of uniform intensity is known, in particular for checking solar panels. For this purpose, filters are mounted on holding devices in a light beam, which consist of a number of mounted wires and influence the light emitted by a lamp.
From U.S. Pat. No. 5,258,895 a device for generating a moire effect is known, in which patterned masks are moved into a light beam for producing the effects.
The same is true for U.S. Pat. No. 4,797,795,from which a lighting device is known, in which different light parameters can be adapted in an automatic and variable way and which in particular relates to the control of such lighting device.
EP 1 331 437 finally discloses a light radiator, which includes, however, no means for variably screening and dimming.